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Quick take
- A complete blood count blood test, often called a CBC, measures the number and characteristics of major blood cells: red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and red blood cell indices such as MCV. MedlinePlus
- A CBC is commonly used as part of routine care, to evaluate symptoms such as fatigue or infection, and to monitor conditions or treatments that can affect blood-cell counts. MedlinePlus
- Most CBC tests do not require fasting, but fasting may be needed if other tests are drawn at the same visit. MedlinePlus
- Abnormal CBC results are clues, not a diagnosis. Your clinician interprets them with your symptoms, medical history, medications, and other test results. Mayo Clinic
- If you buy a CBC directly, compare the effective total cost: test price, provider-charged ordering or physician fees, draw-site rules, mobile collection fees, and whether the order includes a white blood cell differential.
On this page
What is a complete blood count blood test?
A complete blood count blood test is a group of blood measurements that describes the cells circulating in your blood. It is one of the most common laboratory tests because it gives a broad look at oxygen-carrying red blood cells, infection-fighting white blood cells, clot-forming platelets, and several related measurements. MedlinePlus
A CBC can help detect patterns that may fit anemia, infection, inflammation, bleeding or clotting problems, immune conditions, medication effects, or blood disorders. It cannot, by itself, confirm most diagnoses. Mayo Clinic notes that mildly abnormal results may have different significance depending on whether a person has symptoms or is being monitored for a serious condition such as cancer treatment. Mayo Clinic
What does a CBC measure?
The exact report layout varies by laboratory, but most CBC reports include the following measurements. Some orders are written as CBC with differential, which breaks the white blood cell count into types such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
| Result | What it reflects | Why it matters |
|---|---|---|
| Red blood cell count (RBC) | Number of red blood cells | Red blood cells carry oxygen from the lungs to the body. High or low counts can be related to hydration, anemia, bleeding, lung or heart conditions, or other causes. NHLBI |
| Hemoglobin (Hgb) | Oxygen-carrying protein inside red blood cells | Low hemoglobin is a common clue for anemia, but the cause requires context and sometimes additional testing. NHLBI |
| Hematocrit (Hct) | Percentage of blood volume made up of red blood cells | Low hematocrit may fit anemia; high hematocrit may be seen with dehydration or other conditions. NHLBI |
| White blood cell count (WBC) | Total number of white blood cells | High or low WBC counts may occur with infection, inflammation, immune disorders, bone marrow problems, medicines, or other causes. MedlinePlus |
| White blood cell differential | Types and proportions of white blood cells | Helps show which white blood cell type is driving a high or low WBC count. Not every CBC order includes it. |
| Platelet count | Number of platelets | Platelets help blood clot. High or low platelets may be related to bleeding or clotting risk, inflammation, medicines, or bone marrow conditions. Mayo Clinic |
| MCV | Average red blood cell size | Often helps classify anemia patterns, such as smaller-than-usual or larger-than-usual red blood cells. NHLBI |
| MCH, MCHC, RDW | Hemoglobin amount/concentration and variation in red blood cell size | These indices can help clinicians decide whether follow-up iron, B12, folate, inflammation, or other testing is appropriate. |
Why a CBC may be ordered
A clinician may order a CBC for several reasons:
- Routine health assessment: A CBC is often included in general checkups or baseline lab work. MedlinePlus
- Symptoms: Fatigue, weakness, fever, frequent infections, bruising, bleeding, shortness of breath, dizziness, or unexplained weight changes may prompt CBC testing.
- Monitoring: Some medications, chemotherapy, radiation therapy, chronic kidney disease, inflammatory conditions, and known blood disorders can affect blood-cell counts.
- Follow-up: An abnormal CBC may lead to repeat testing, a blood smear, iron studies, vitamin B12 or folate testing, inflammatory markers, kidney testing, or a hematology referral depending on the pattern.
How to prepare for a CBC blood test
For a CBC alone, special preparation is usually not needed. A health professional typically draws a small blood sample from a vein in your arm, and the draw usually takes only a few minutes. MedlinePlus
Preparation can change if your CBC is ordered with other labs. For example, a lipid panel or some glucose-related tests may come with fasting instructions. Follow the instructions on your lab order or from the ordering clinician.
Before your appointment
- Drink water unless you were specifically told to restrict fluids.
- Bring identification and your lab order or confirmation code if you ordered online.
- Tell the ordering clinician about medicines, supplements, recent illness, pregnancy, heavy exercise, high-altitude exposure, recent bleeding, or transfusion history if those are relevant.
- If you tend to faint during blood draws, tell the phlebotomist before the needle stick.
How to read CBC results
CBC reports show your value, the unit of measurement, and a reference range. Reference ranges vary by laboratory and can differ by age, sex, pregnancy status, altitude, and other factors. NHLBI provides examples of common adult ranges, but your own report’s reference interval is the one your clinician will usually use. NHLBI
| Measurement | Example adult reference range | Important note |
|---|---|---|
| RBC | Adult men: 5–6 million cells/mcL; adult women: 4–5 million cells/mcL | Ranges vary and may be influenced by altitude and other factors. |
| WBC | 4,500–10,000 cells/mcL | Differential results can be more informative than total WBC alone. |
| Platelets | 140,000–450,000 cells/mcL | Platelet trends may matter as much as one result. |
| Hemoglobin | Adult men: 14–17 g/dL; adult women: 12–15 g/dL | Low values may fit anemia, but additional testing is often needed to identify the cause. |
| Hematocrit | Adult men: 41%–50%; adult women: 36%–44% | Hydration status can affect hematocrit. |
| MCV | Commonly reported in femtoliters | Low or high MCV can help classify red blood cell patterns. |
Common result patterns
- Low hemoglobin, hematocrit, or RBC: Often raises the question of anemia. Causes can include iron deficiency, vitamin deficiency, blood loss, chronic inflammation, kidney disease, inherited blood conditions, and other issues. Mayo Clinic
- High hemoglobin, hematocrit, or RBC: May be related to dehydration, smoking, high altitude, lung or heart disease, testosterone therapy, or bone marrow disorders, depending on context.
- High WBC: Often occurs with infection or inflammation, but medicines, stress, vigorous exercise, immune conditions, or some blood disorders can also contribute. MedlinePlus
- Low WBC: Can be associated with some infections, autoimmune conditions, bone marrow disorders, cancer treatments, or medications. MedlinePlus
- High or low platelets: May reflect inflammation, bleeding, clotting disorders, medication effects, iron deficiency, immune conditions, or bone marrow conditions. Mayo Clinic
When to seek prompt medical help
Do not wait for routine follow-up if you have severe shortness of breath, chest pain, fainting, uncontrolled bleeding, black or bloody stools, confusion, a high fever with worsening symptoms, or a CBC result that your lab or clinician flags as critical. Use urgent or emergency care when symptoms are severe.
What a CBC does not measure
A CBC does not directly measure liver enzymes, kidney filtration, glucose, cholesterol, thyroid hormones, iron stores, vitamin B12, folate, inflammatory markers, or infection-specific organisms. It may suggest that follow-up testing is reasonable, but it is not a complete wellness panel by itself. If you are comparing lab packages, check whether you are buying CBC only, CBC with differential, or a broader panel that includes tests such as a comprehensive metabolic panel.
Direct-pay CBC options: what to compare
Some people get a CBC through a clinician, while others use direct-pay lab ordering services. In the United States, clinical laboratory testing is regulated under CLIA standards intended to support accurate, reliable, and timely lab results. CMS
If you order a CBC yourself, compare the total checkout cost and the actual test configuration. A lower list price may not be the lowest effective price if a provider-charged ordering fee, lab processing fee, or mobile collection fee applies. when you want to review current direct-pay options side by side.
| Example option | What the public page lists | Collection network | Provider fees and ordering notes |
|---|---|---|---|
| Quest Health CBC | $29.00 list price for CBC; page states the test measures RBCs, WBCs, hemoglobin, hematocrit, and platelets. | Quest Diagnostics patient service center; Quest Mobile may be available in some areas. | The CBC page shows a $6.00 physician service fee and states that in-home collection, where available, costs an additional $79. The page also notes age and location restrictions may apply. |
| Labcorp OnDemand CBC | $29 for a CBC with differential; page states no special preparation is needed. | In-person blood draw at a Labcorp location. | The page states an authorized healthcare professional order is required through Labcorp OnDemand’s contracted provider process, with results accessed through a Labcorp Patient account. |
Methodology for comparing cost to the patient
For direct-pay CBC options, compare: (1) listed test price, (2) provider-charged mandatory ordering or physician fees, (3) separate lab processing or draw fees if shown, (4) mobile or home-draw charges if selected, (5) whether insurance is billed or the order is self-pay only, (6) whether the test includes a differential, and (7) state, age, and collection-site restrictions. Do not compare a CBC-only test with a broad wellness membership or multi-test panel as if they were the same product.
Questions to ask about your CBC
- Was this a CBC only, or a CBC with differential?
- Which results are outside the reference range, and are they mildly or significantly abnormal?
- Are my results new, or have they appeared on previous CBC tests?
- Could recent illness, hydration, exercise, menstruation, pregnancy, altitude, medicines, or supplements affect the result?
- Do I need repeat testing, a blood smear, iron studies, B12, folate, kidney testing, inflammatory markers, or another follow-up test?
- Should any result be reviewed urgently?
FAQs
What is a complete blood count blood test used for?
A complete blood count blood test is used to evaluate the major cells in your blood. It may be part of routine care, symptom evaluation, or monitoring for conditions and treatments that affect blood counts. MedlinePlus
Do I need to fast before a CBC?
Usually no. A CBC alone generally does not require fasting. If other tests are ordered from the same blood draw, follow the fasting instructions for those tests. MedlinePlus
What is the difference between CBC and CBC with differential?
A standard CBC includes the total white blood cell count. A CBC with differential also measures the different types of white blood cells, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils. That breakdown can help clarify why the total WBC is high, low, or changing.
Can a CBC diagnose anemia?
A CBC can show low hemoglobin, hematocrit, or red blood cell count, which may fit anemia. It usually cannot identify the exact cause by itself. Iron studies, ferritin, B12, folate, reticulocyte count, kidney tests, or other evaluations may be needed.
Can a CBC detect cancer?
A CBC may show patterns that raise concern for certain blood or bone marrow disorders, but it is not a general cancer screening test. Abnormal results require clinical interpretation and may need additional testing. Mayo Clinic
How long do CBC results take?
Turnaround time varies by lab and ordering route. Some direct-pay CBC pages list results in about 1 day or 1–2 business days after sample processing and clinical review, but timing can vary by location, weekends, and whether follow-up review is needed. Labcorp OnDemand Quest Health
Is a slightly abnormal CBC always serious?
No. Mildly out-of-range results can occur for many reasons, including hydration, recent infection, medicines, menstrual bleeding, exercise, or normal biologic variation. MedlinePlus emphasizes that abnormal CBC levels do not always mean a medical condition needs treatment. MedlinePlus
Bottom line
A CBC is a high-value screening and monitoring test because it summarizes several major blood-cell systems in one report. The most useful next step is not to interpret one flagged value in isolation, but to look at the pattern: red cell measures, white cell count and differential, platelet count, symptoms, medications, and prior results. If you are paying out of pocket, compare the exact test type and the provider’s total checkout cost, including any fees charged by the provider.
Sources
- MedlinePlus: Complete Blood Count (CBC)
- National Heart, Lung, and Blood Institute: Blood Tests
- Mayo Clinic: Complete Blood Count (CBC)
- CMS: Clinical Laboratory Improvement Amendments (CLIA)
- Quest Health: Complete Blood Count (CBC) Test
- Labcorp OnDemand: Complete Blood Count (CBC) Test
Use the CTX Stat nationwide comparison tool to review self-pay prices across major laboratory testing providers.
